1. Field of the Invention
The present invention relates to a manufacturing facility for a steel member, a thin bearing-member namely a thin member for a bearing, and a thrust bearing. More specifically, the invention relates to a steel-member manufacturing facility that can easily be automated, a thin bearing-member that is manufactured by the steel-member manufacturing facility, and a thrust bearing having the thin bearing-member.
2. Description of the Background Art
Generally, for a thin bearing ring/washer which is a steel member, such a material as SPCC (JIS G 3141 standard) that is a low-carbon steel or SCM415 (JIS G 4053 standard) is employed. These materials are formed into a required shape and thereafter subjected to a short-term carburizing process and subsequently to a quenching process. Accordingly, the materials are quench-hardened, namely hardened by quenching to ensure hardness of a level required for the ring/washer. In some cases, such a high-carbon steel material as SUJ2 (JIS G 4805 standard) or SAE1070 is also employed as a material for the ring/washer. In this case, these materials are formed into a required shape, thereafter heated in a controlled atmospheric furnace and subsequently rapidly cooled and thereby quench-hardened. In this way, hardness of a level required for the ring/washer is ensured.
In terms of efficient operation of the heat treatment furnace and the quenching apparatus, the above-described quench-hardening is performed through batch treatment under which heat treatment is performed lot by lot comprised of an appropriate number of steel members (rings/washers).
In some cases, for the quench-hardening of the ring/washer, induction hardening is also employed using induction heating to heat and quench the ring/washer. The induction hardening can extremely shorten the process time as compared with quenching using a controlled atmospheric furnace for example. Thus, the induction hardening can contribute to improvement of production efficiency especially in the case where one lot includes a relatively small number of steel members.
In recent years, such a product as automobile using a bearing having the thin bearing ring/washer has been being enhanced in performance and functionality. Under this situation, the level of characteristics required for the bearing is becoming higher. Further, in terms of improvement of price competitiveness, cost reduction is also an important object to be achieved.
Under the circumstances, a method of determining whether or not induction hardening has normally been performed (see for example Japanese Patent Laying-Open Nos. 11-031579 and 09-118917), a method of efficiently performing induction hardening (see Japanese Patent Laying-Open Nos. 09-031532 and 05-263125) and an apparatus for measuring the hardening depth of an induction-hardened member (see Japanese Patent Laying-Open No. 2004-177159) for example have been proposed.
Further, the thin bearing ring/washer used for the bearing is likely to be distorted while quenched in the manufacturing process. In the case where the ring/washer is distorted to a considerable degree, the bearing having the distorted ring/washer has a shortened lifetime.
Then, as a method of suppressing distortion of a steel material while being quenched, a method has been proposed according to which the scale thickness on the surface of the steel plate while the steel plate is being press-quenched is set to 10 μm or less. Accordingly, a component formed to have superior shape precision can be manufactured (see Japanese Patent Laying-Open No. 2003-231915). Further, a method has been proposed, regarding the press quenching of a steel material, according to which the steel material in the state constrained, namely prevented from distorting, by molds is immersed in a cooling fluid (see Japanese Patent Laying-Open No. 07-157822). Accordingly, distortion and bending occurring in the quenching process can be reduced even for a high-hardness steel material. Furthermore, a method has been proposed according to which the outer periphery as well as the end surfaces in the width direction of a thin ring are constrained by means of a collet (constraining member) to perform quenching. Accordingly, distortion occurring in the quenching process is suppressed (see Japanese Patent Laying-Open No. 05-033060).
The above-described measures to make improvements concerning the induction hardening contribute to improvements in quality and reduction in cost of the steel member. However, since a conventional quenching apparatus including an induction hardening apparatus frequently uses oil or water for example as a cooling medium for quenching, other apparatuses for processing and testing are installed in many cases at locations remote from the quenching apparatus for the purpose of avoiding influences of the oil or water. Consequently, there arises a necessity to convey the steel member between the quenching apparatus and other apparatuses, resulting in deterioration in production efficiency and increase in manufacturing cost. Moreover, the steel member, especially the one before quench-hardened, is likely to be deeply flawed while the steel member is being conveyed, due to low hardness of the steel member, which could cause defective products.
In addition, even in the case where the above-described method of suppressing distortion is applied to a thin bearing ring/washer to produce a bearing, the resultant bearing is not necessarily sufficiently long in lifetime, in consideration of the recent demands for higher-level characteristics.